refactor(cpus): convert checker functions to standard helpers

The library check_erratum_ls already incorporates the check. The return
of ERRATA_MISSING is handled in the errata_report.c functions.

Change-Id: Ic1dff2bc5235195f7cfce1709cd42467f88b3e4c
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
(cherry picked from commit b54771678d0db79c709a7b379b107ea4546b33fe)
2 files changed